Low voltage dc control of voltage-variable capacitors

ABSTRACT

This disclosure covers voltage-variable capacitors, and circuits for applying a control voltage to voltage-variable capacitors. More particularly, this disclosure is of circuits for connecting a plurality of voltage-variable capacitors to be actuated by a common control voltage.

United States Patent Inventor Appl. No. Filed Patented Assignee DOWVOLTAGE DC CONTROL OF VOLTAGE- [56] References Cited UNITED STATESPATENTS 2,802,171 8/1957 Minder 323/93X 3,470,446 9/ l 969 Berry et al.323/93X Primary Examiner-J. D. Miller Assistant Examiner-G. GoldbergAttorneys-Harry M. Saragovitz, Edward J. Kelly, Herbert Berl and CharlesF. Gunderson VARIABLE CAPACITORS 3 Claim, 3 Drawing Figs.

US. Cl. 323/74,

317/255, 323/93 ABSTRACT: This disclosure covers voltage-variablecapaci- Int. Cl "02m 5/08, s and circuits for applying a control voltageto voltage-vari- HOZp 13/00 able capacitors. More particularly, thisdisclosure is of circuits Field of Search 323/74, 93; for connecting aplurality of voltage-variable capacitors to be 3 l 7/255; 333/ l 9, 70R;33 l/36C actuated by a common control voltage.

8 CONTROL VOLTAGE AeC CIRCUIT 7 IOR PATENTEDFEB, 9m O Y 3562,63?

. CONTROL VOLTAGE I2 l4 I i A-C v I3 I CIRCUIT B C D 7 10R 12R 14R 0 2CONTROL VOLTAGE 24 v F K FIG. 3 o

1 CONTROL VOLTAGE 3IR 33R 35R 31 M N 33 o P 35 INVENTOR, EMANUEL GIKOW mAGENT 4n W) m 3% vL ATTORNEYS,

LOW VOLTAGE DC CONTROL OF VOLTAGE- VARIABLE CAPACITORS BACKGROUND OF THEINVENTION 2 Voltage-variable capacitor are well known and include, forexample, certain dielectric types of capacitors, and the "Varicap"types. The capacity of the dielectric types can be controlled by varyingthe potential gradient across the dielectric which changes thedielectric constant. The capacity of the Varicap types, which arebasedon a semiconductor material that exhibits a capacity across a junction,can be controlled by varying the potential of a control voltage of agiven polarity across the junction.

Certain types of voltage-variable capacitors are advantageous forcertain purposes, but all have limitations as to the-available capacity,or limitations as to the tolerable, alternating signal voltage that canbe accommodated by the capacitor, or the amount of control voltage thatmay be needed to provide the necessary degree of capacitance variation.They are also limited in some cases, where the applied signal voltagehas an appreciable'efi'ect on the control voltage and shifts theeffective capacity in an undesired manner.

It is therefore an object of this invention to provide a circuit thatwill extend the useable limits of voltage-variable capacitors.

It is a further object of this invention to provide a circuit that willgive a wider range of control of capacity for a given control voltage.

SUMMARY OF THE INVENTION A plurality of voltage-variable capacitors areconnected in series circuit requiring a variable, capacitive reactance.One polarity of a control voltage is connected to the odd junctions ofthe series connection of voltage-variable capacitors, and the otherpolarity of the control voltage is connected to the even junctions ofthe series connection of voltage-variable capacitors. This provides avery much greater control of the overall capacity with acomparativelylow DC value of control-voltage and comparatively lesschange in control-voltage for a given change in capacity.

BRIEF DESCRIPTION OF THE DRAWING The three FIGS. in the drawing showcircuit diagrams of typical connections of a source of control voltage.to a series connection of voltage-variable capacitors for use in analternating-current circuit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a circuitdiagram withwoltage-variable capacitors A through D connecting seriesacross the terminals 6 and 7 of an AC circuit or utilization circuit.The junctions of the voltage-variable capacitors are numbered,consecutively, 10 through 14. A source of control voltage is appliedacross the terminals 8 and 9, with one potential of the sources ofcontrol voltage connected to the even junctions of the series connectionof voltage-variable capacitors through resistors that are numbered 10R,12R, and 14R to correspond with the junctions. The other potential ofthe source of control voltage is connected to the odd junctions of theseries connection of voltage-variable capacitors through resistors thatare, again, correspondingly numbered 11R and 13R.

In operation, as the single control voltage is varied, it varies thecapacitance of all of the voltage-variable capacitors in the series.This produces a corresponding effect on the overall capacity across theterminals 6 and 7 of the utilization circuit.

' FIG. 2 shows another series of voltage-variable capacitors E, F, G,and II, and with their series junctions consecutively numbered 20through 24. The voltage-variable capacitors are connected-throughdecoupling capacitors J and K-across the terminals 6 and 7 of analternating-current circuit or utilization circuit. A source of controlvoltage is applied across the terminals 8 and 9 as before. One potentialof the source of control voltage is, again, connected to the evenjunctions of the series connection of voltage-variable capacitorsthrough resistors that are numbered 20R, 22R, and 24R and the otherpotential of the source of control voltage is connected to the oddjunctions through resistors 21R, 23R to correspond to the numbering ofthe terminals.

In FIG. 2 it is noted that the alternating current circuit is not indirect contact with voltage-variable capacitors or their control voltagepotentials, but is isolated by the decoupling capacitors .I and K. Thesemay be conventional capacitors rather than voltage-variable capacitors,since only one potential of the source of control voltage is applied tothem. Capacitors J and K would, normally, have no effect on the ACcircuit, but they may be of values that will have an effective reactanceat the frequencies involved if desired.

FIG. 3 shows a connection of voltage-variable capacitors L through P,again in series, across the terminals 6 and 7 of a utilization circuit.The. junctions of the voltage-variable capacitors are numbered,sequentially, 30 through 35 and, again, the source of control voltage atterminals 8 and 9 has one polarity connected to the even numberedjunctions through even numbered resistors, and the other polarity of thesource of control voltage is connected to the odd numbered junctionsthrough odd numbered resistors.

In the case of FIG. 3, the opposing polarities, rather than the samepolarity, of the source of control voltage are connected to the opposingterminals of the utilization circuit, which may be desirable for certainpurposes.

The operation of these species of FIGS. 2 and 3 is the same as that ofFIG. I with the exception of the differences in any effect of thecontrol voltage on the utilization circuit or vice versa.

The resistors, in all of these species, must all be of a high enoughvalue, with respect to the capacitive reactance across the terminals 6and 7, to have negligible effect on the rest of the circuit. The sameisolation from the rest of the circuit may also be provided by inductorsof sufficient inductive reactance for the frequencies involved.

The potential and the change of potential of the control voltage must bewithin the limits prescribed for the type of voltage-variable capacitorsbeing used.

The polarity of the control voltage is not indicated since it depends onthe voltage-variable capacitors being used. If they are of thedielectric types, for example, that are not polarity sensitive, it doesnot matter which polarity is applied to either of the terminals. If thecapacitors are of the Varicap type, for example, that are polaritysensitive, the orientation of the capacitors must be in accordance withthe polarity of the control voltage connection.

Other voltagevariable capacitors can be added in parallel with some orall of the capacitors of the series in a well known manner to add moreoverall capacity when needed.

In a typical, variable, capacitive circuit in accordance with FIG. I,the voltage-variable capacitors A through D may have a dielectric oflead strontium titanate, with one-eighth inch diameter electrodes spaced3.5 mils apart. A change of control voltage at terminals 8 and 9 from 0to 350 volts will cause a change in capacity of from I50 to 25picrofarads across terminals 6 and 7. The resistors should all be in theorder of 20,000 ohms at l megacycle.

I claim:

1. A circuit for controlling voltage-variable capacitors comprising aplurality of voltage-variable capacitors connected in series; saidplurality of voltage-variable capacitors having alternate, odd and evenjunctions between said capacitors in said series; a source of controlvoltage; means for connecting one polarity of said source of controlvoltage to said odd junctions of said voltage-variable capacitors; meansfor connecting the other polarity of said source of control voltage tosaid even junctions of said voltage-variable capacitors; and means forconnecting said series of voltage-variable capacitors into an ACelectric circuit.

2. in a circuit as in claim 1 said means for connecting said source ofcontrol voltage to said odd and said even junctions of saidvoltage-variable capacitors comprising a plurality of resistors, eachhaving a value substantially higher than the capacitive impedance ofsaid voltage-variable capacitors, and each of said resistors connectingone of said junctions to the

1. A circuit for controlling voltage-variable capacitors comprising aplurality of voltage-variable capacitors connected in series; saidplurality of voltage-variable capacitors having alternate, odd and evenjunctions between said capacitors in said series; a source of controlvoltage; means for connecting one polarity of said source of controlvoltage to said odd junctions of said voltage-variable capacitors; meansfor connecting the other polarity of said source of control voltage tosaid even junctions of said voltage-variable capacitors; and means forconnecting said series of voltage-variable capacitors into an ACelectric circuit.
 2. In a circuit as in claim 1 said means forconnecting said source of control voltage to said odd and said evenjunctions of said voltage-variable capacitors comprising a plurality ofresistors, each having a value substantially higher than the capacitiveimpedance of said voltage-variable capacitors, and each of saidresistors connecting one of said junctions to the appropriate polarityof said source of control voltage.
 3. In a circuit as in claim 1, saidAC, electrical circuit having a pair of terminals; and said means forconnecting said series of voltage-variable capacitors into said AC,electrical circuit comprising a first capacitor cone connecting one endof said series of voltage-variable capacitors to one terminal of saidAC, electrical circuit, and a second capacitor connecting the other endof said series of voltage-variable capacitors to the other terminals ofsaid AC electrical circuit.